The invention relates to selecting optical waves.
Various systems use electromagnetic waves whose spectral content is in the optical portion of the electromagnetic spectrum, called “optical waves” or “light waves.” The optical portion of the electromagnetic spectrum includes, for example, the visible spectrum, the infrared (IR) spectrum, and the ultraviolet (UV) spectrum. Optical waves can propagate in non-guided spatial modes (or “free space” modes) within an optical system, or in guided spatial modes within guiding media such as optical fibers or waveguides in optical devices. An optical combining device can combine multiple optical waves such that they propagate along the same propagation axis and, in some cases, in the same spatial mode. An optical splitting device can separate optical waves from a wave received over an optical input port based on properties such as wavelength, spatial mode, or polarization. Some devices can both combine and separate different optical waves, such as an add-drop multiplexer, which drops and adds optical waves based on wavelength.
Some devices can act as either a combiner or splitter. For example, a polarizing beam splitter (PBS) can split an optical wave entering a first port into a vertically polarized optical wave from a second port and a horizontally polarized optical wave from a third port. Alternatively, the PBS can combine a vertically polarized optical wave entering the second port and a horizontally polarized optical wave entering the third port to leave the first port having the same propagation axis.
Some applications call for an “optical cross-connect” or “optical switching circuit” that connects a given optical input port to a given optical output port based on one or more control signals. A desired optical wave can be selected by providing a high transmission optical path from the corresponding input port to the output port. For example, some micro-electro-mechanical systems (MEMS) devices tilt mirrors in response to control signals to select which of multiple optical input ports to direct to a given optical output port.